Field of the Invention
The present invention relates to an apparatus for taking close-up pictures by using a camera and an LED illumination which are embedded in a mobile terminal such as a smart phone, and to an exterior optical module for taking the close-up pictures.
Description of the Related Art
Mobile terminals, such as smart phones and tablet computers, which are widely used recently, are equipped with exposed cameras and LED illumination for taking pictures of external subjects. Users take pictures by only using a camera, or, when an illumination is required, take pictures after controlling an LED to be turned on. Accordingly, the camera and the LED illumination are provided adjacent to each other on one surface of a mobile terminal.
In general, the camera embedded in a mobile terminal has an auto focus (AF) function such that the focal length thereof is changed by changing the distance between an embedded lens and an image sensor. Here, the minimum focal length is set for each camera embedded in the mobile terminal, and the shortest photographing distance is set according to the minimum focal length. When a subject is located within the shortest photographing distance, the subject may not be photographed or an unclear image is obtained because the subject is out of focus.
In order to photograph a subject within the shortest photographing distance, the subject may be photographed at a distance about the minimum focal length with a predetermined optical magnification ratio, and a digital zoom may be used through a digital image processing method. However, in such cases, the image contrast is remarkably decreased and thus the state of the subject can not be well viewed.
Recently, there have been attempts to take a close-up picture of the skin tissue of a user by using a camera embedded in a mobile terminal, for skin care purposes. The shortest photographing distance of embedded cameras in mobile terminals are about 50 mm or more, and the state of skin tissues may not be clearly viewed through the images taken from such a distance even when a digital zoom is applied. In other words, a clearly in-focus and magnified image by achieving a shorter photographing distance to shoot at a closer distance is required.
As the best method for taking close-up pictures, the method in which the camera which itself embedded in a mobile terminal is designed to embed various lenses together therein so as to further decrease the shortest photographing distance may be a fundamental solution. The problem is that such a fundamental solution has not yet been developed, probably due to the effect that the solution has in determining the product price. Most of all, mobile phones developed up to now can not be used to take pictures in such a manner.
Alternatively, a method in which a macro lens is attached to the outside of a mobile terminal may be used. This method photographs the state of the skin by using external light such as natural light or indoor lighting. Accordingly, in this case, close-up pictures are not uniform, and in some cases, it may be impossible to take pictures or the pictures taken may be unsuitable. For example, in the case of a backlight in which an illumination is located at the rear side of a subject, the image of the subject is not well formed because too much amount of light enters the camera. Also, when the surroundings are too dark, it may be impossible to take a picture due to insufficient illumination.